DESCRIPTION: The University of Washington is the applicant organization with a subcontract to the University of Lisbon, Portugal, as the clinical site. A randomized clinical trial is proposed in which 500 children (400 by the end of the study) of ages 8 to 10 who are students of Casa Pia Schools in Lisbon, Portugal, and who need extensive dental restorative treatment are provided care while randomized to the use or non-use of dental amalgams in their treatment. Exposure to mercury from dental amalgams will be measured from urine samples obtained at baseline and follow-up exams at one-year intervals for up to five years. Six primary endpoints will be monitored from baseline at one-year intervals: three neurobehavioral (combined assessments from neurobehavioral test for attention, memory, and motor/visual motor domains); one neurological (nerve conduction velocities); and two renal (two Glutathione Transferase isozymes specific to proximal and distal renal tubular damage). In addition, a potential secondary endpoint (immunologic) will be monitored, via a urinary dip stick analysis on site at the time of each urine collection. Should indications of glomerular damage be found on repeated testing, a complete urinalysis, including tests for antinuclear antibodies (ANA) and circulating immune complexes (CIQ), would be conducted. Comparison between the two groups of children for the six primary endpoints will be made annually using an extension of the O'Brien test for multiple endpoints adapted for longitudinal data and multiple tests over time. If significant adverse health effects of exposure to dental amalgams (or to the alternative dental material, composites) are detected during the course of the study, the children treated with the harmful material will be re-treated with the other. This study is designed to settle the controversy over whether the most commonly-used dental material in the world, dental amalgam, has even any subtle health effects associated with its use in perhaps the most susceptible population, children.